In multilayer packaging, various layers are often combined to provide a final product that has the characteristics of the separate layers. Structures that include different types of polyethylene, polypropylene, and ethylene vinyl acetate together with barrier layers such as ethylene vinyl alcohol (EVOH) and polyamide (PA) are often used in number of applications, including packaging. For example, these types of structures may be used in food packaging applications for meat and cheese. In such multilayer constructions, polypropylene typically provides stiffness, temperature resistance and scuff resistance. Polyethylene typically provides clarity and tear resistance, seals at a lower temperature and is softer than polypropylene. Styrene polymers can be included in such structures to provide structural integrity. In designing multilayered structures, adhering the separate layers to one another is a challenge that must be addressed. This is particularly the case for structures containing both polypropylene and polyethylene layers, and also styrene polymer layers in thermoforming applications together with barrier layers. There is a need to develop a product that utilizes a single type of tie layer in a multilayer structure because in a commercial setting, the capital investment that would be required for multiple extruders, and additional extrusion steps translate to higher operating costs.
U.S. Patent Publication No. 2007/0167569 discloses adhesives containing styrene-isoprene-styrene polymers in multilayer structures containing styrene polymer layers. U.S. Patent Publication No. 2009/0171022 discloses adhesives containing styrene-isoprene-styrene/styrene-butadiene-styrene polymer blends in multilayer structures containing styrene polymer layers. U.S. Pat. No. 6,184,298 discloses adhesives containing unmodified styrene-based elastomers in multilayer structures containing polyethylene and polypropylene. However, a continuing need exists for multilayer structures containing layers of polyethylene, propylene polymers, and styrene polymers, having a common tie layer with the capability of adhering all layers in the structure.